Field of the Invention
The present invention relates to a method of simultaneous laser welding of an automotive light and relative automotive light obtained using said method.
Description of the Related Art
The term automotive light is understood to mean indifferently a rear automotive light or a front automotive light, the latter also known as a headlight.
As is known, an automotive light is a lighting and/or signalling device of a vehicle comprising at least one external automotive light having a lighting and/or signalling function towards the outside of the vehicle such as for example a sidelight, an indicator light, a brake light, a rear fog light, a reverse light, a dipped beam headlight, a main beam headlight and the like.
The automotive light, in its simplest form comprises a container body, a lenticular body and at least one light source.
The lenticular body is placed so as to close a mouth of the container body so as to form a housing chamber. The light source is arranged inside the housing chamber, which may be directed so as to emit light towards the lenticular body, when powered with electricity.
The method of manufacture of an automotive light, once assembled the various components, must provide for the attachment and hermetic sealing of the lenticular body to the container body.
Such sealing and attachment is usually performed by welding so as to create a weld bead between the perimetral profiles, respectively, of the lenticular body and the container body placed in contact with each other.
Naturally, the welding may also regard other components of a more complex automotive light, for example arranged inside the housing chamber.
A process of laser welding of polymeric bodies particularly of an automotive light makes it possible to combine a transmissive or transparent polymeric body, capable of transmitting a laser radiation, and an absorbent polymeric body, capable of absorbing the laser radiation. In the present case, the laser radiation is transformed into heat when it encounters the absorbent polymeric body which heating locally transfers heat to the transmissive polymeric body, as far as a softening and a local melting of both polymeric bodies, which thus join firmly to each other.
The absorbent polymeric body of an automotive light may be constituted, for example, by the container body, while the transmissive polymeric body of a automotive light may be constituted, for example, by the lenticular body, which closing the container body forms a housing chamber housing a light source of the automotive headlight.
The housing chamber is delimited at the perimeter by the perimetral profiles of the container body and of the lenticular body which, placed in contact with each other, are sealed by the formation of a weld bead, at which the interpenetration of the materials of the lenticular body and the container body takes place.
Of course, the absorbent and transmissive polymeric bodies can be composed generically by further polymeric components of the automotive headlight.
The laser equipment that is typically used for this purpose generally includes:                at least a laser source, which can for example be a semiconductor laser source,        a system of optical fibres grouped together in a “bundle” which serves to transport the laser light produced by the laser source, in the vicinity of the lenticular body,        an optical fibre support which has the purpose of holding the optical fibres in position in the vicinity of the lenticular body. For example, the support may be a metal body with housing holes in which the optical fibres are contained. They may be attached by a system in which the head of a screw, which is screwed to the metal support of the optical fibres, presses a polymer washer which expands radially. The optical fibre is thus blocked by the polymer washer on the housing hole walls,                    an optical system, with the function of a collimator, which has the purpose of modifying the divergence of the laser beam coming out of the fibre and directing said beam towards the weld bead.                        
Typically, as a collimator, a negative light guide is used, i.e. a light guide formed of reflective walls.
In the simplest version of the prior art, the light guide has a geometry with reflecting walls inclined with respect to its optical axis and the optical fibre is positioned in the vicinity of the upper opening of the light guide and along the optical axis. Again in the simplest case, the system proves to be symmetric on the transversal plane of the light guide, i.e. the inclination of the reflective walls of the light guide is the same with respect to the optical axis. Longitudinally, the light guide extends along the trajectory which defines the weld bead.
Alternatively, the light guide may be made of a solid polymer body and fitted with reflective internal walls, able to direct the laser radiation inside said polymer body by multiple reflections.
In some applications, such as those typical of automotive lights, the light guide rests an outlet opening thereof, which emits laser radiation, along a multiform support trajectory, made on an outer surface of the lenticular body transparent to laser radiation. The latter is placed adjacent to a container body absorbing the laser radiation, so as to define the weld bead, also multiform, and typically dissimilar from the multiform support trajectory.
It is to be noted that the light guide lying on the lenticular body could direct the laser radiation towards a weld bead defined by at least one polymer component to be welded extraneous to said lenticular body and/or said container body, contained however in an area bounded by the latter.
The light guide of the conventional simultaneous laser welding apparatus extends without interruption on the outer surface of the lenticular body at the weld bead, in an effort to reach it with sufficient energy to soften the container body, thereby enabling the welding process. The laser radiation coming out from the opening of the light guide may however undergo refraction during its entry into the lenticular body, as well as one or more reflections inside the lenticular body itself, before reaching the weld bead.
Unfortunately, in automotive light applications it happens that the laser radiation coming out from the exit aperture of the light guide reaches the weld bead heterogeneously, with sections of the weld bead reached by insufficient energy to soften the container body. This is caused by the fact that the geometry of the lenticular body is typically complex, including on account of the presence of ribs, changes of curvature or the like, and the weld bead extends in a multiform manner.
Lenticular bodies tend, in fact, for stylistic and aerodynamic reasons to be increasingly complex and to have on their outer surface, surfaces with discontinuities such as ribs, chamfers, fillets, draughts, etc. The complex shape of the lenticular bodies and discontinuities present on the surface of the lenticular body may make the transposition of the laser beam from the optical fibre to the weld bead difficult and inefficient despite the action of the light guide.
In fact on account of the complex shape of the lenticular body, the weld bead proves not conformal to the lenticular body, i.e. it may not be a translation of the lenticular body.
It is clear that if the weld bead is unevenly reached by the laser radiation, an increase in the power of the laser radiation, to overcome the lack in the portions poorly irradiated would be excessive in the portions of the weld bead irradiated sufficiently, with the risk of damage to portions of the lenticular body and the container body.
It follows that, in the case of simultaneous welding of automotive lights where the lenticular body usually has complex geometries (such as variations of concavities/complexity, grooves, ribs, protuberances, and the like), the solutions of the prior art of laser welding are not satisfactory in terms of quality of the weld bead generated.
In the light of all the above considerations, laser welding techniques are little used to date on automotive lights, especially if they have a complex geometry; such laser welding techniques are thus replaced by alternative welding techniques, such as friction, ultrasonic, hot-plate welding and the like.